Zoom lens and image pickup apparatus having the same

ABSTRACT

A zoom lens includes a first, third and fourth lens group of positive refracting power, a second lens group of negative refracting power, wherein, during zooming from a wide-angle end to a telephoto end, at least the first lens group moves, wherein the third lens group includes, a first lens sub-group of positive refracting power and a second lens sub-group of negative refracting power, wherein the second lens sub-group includes a single negative lens, wherein the first lens sub-group of the third lens group is moved to keep a perpendicular component relative to an optical axis to correct image blur to be produced when the zoom lens vibrates, and wherein, when a focal length of the first lens group is denoted by f1 and the focal length of the whole system at the wide-angle end is denoted by fw, a conditional expression 10.0&lt;f 1 /fw&lt;20.0 is satisfied.

FIELD OF THE INVENTION AND RELATED ART

This invention relates to a zoom lens and an image pickup apparatushaving the same. The present invention is suitably applicable to a videocamera, electronic still camera, TV camera (broadcast camera), andsilversalt photographic camera, for example.

In recent years, the image pickup apparatus such as a video camera,digital still camera or broadcast camera using a solid-state imagepickup device, or a camera using a silver film, has been designed tohave a higher function and smaller size.

With regard to the photographic optical system to be used in such imagepickup apparatus, it is required that the lens overall length is shortand compact, the zoom ratio is high and the resolution is highthroughout the whole zoom range.

As a zoom lens which meets these requirements, there is a zoon lenscalled a rear focus type in which the focusing is carried out by movinga lens group or groups other than the first lens group which is placedclosest to the object side.

Generally, as compared with the front focus type zoom lens in which thefirst lens group is moved to perform the focusing, the rear focus typezoom lens has an advantage that, since the effective diameter of thefirst lens group can be made smaller, reduction in size of the wholelens system is easy. Furthermore, the macro-photography is easy.Moreover, since the focusing is carried out by moving a lens group whichis small in size and light in weight, the driving force for the lensgroup is small and quick focusing is possible.

As such rear focus type zoom lens, there is a four-group zoom lens whichis comprised of, in an order from the object side to the image side, afirst lens group of positive refracting power, a second lens group ofnegative refracting power, a third lens group of positive refractingpower, and a fourth lens group of positive refracting power.

U.S. Pat. Nos. 7,206,137 and 7,190,529 show a four-group zoom lens inwhich all the lens groups are moved to perform the zooming.

As a rear focus type zoom lens, there is a five-group zoom lens which iscomprised of, in an order from the object side to the image side, firstto fifth lens groups having positive, negative, positive, positive andpositive refracting powers, respectively.

U.S. Pat. No. 5,530,592 shows a five-group zoom lens in which the secondand third lens groups are moved for the zooming, while the image planechange due to the power change is corrected by moving the fourth lensgroup. Furthermore, the focusing is carried out by moving the fourthlens group.

On the other hand, if vibration occurs in the zoom lens when aphotogenic subject is being photographed, it results in blurring in theimage photographed. In consideration of this, various zoom lenses havinga vibration control function for correcting the blur of the photographedimage have been proposed.

Among these proposals, there is a four-group zoom lens in which thethird lens group is comprised of two lens groups one of which isoscillated in a direction perpendicular to the optical axis (JapaneseLaid-Open Patent Application No. 10-232420, U.S. Pat. No. 6,266,189 andJapanese Laid-Open Patent Application No. 2002-244037).

Generally, in order to reduce the size of a zoom lens, the number of thelenses constituting the zoom lens should be decreased whilestrengthening the refracting power of each lens group. However, in suchzoom lens, the lens thickness increases with the increase of therefracting power of each lens surface. Thus, the length shorteningeffect of the whole lens system becomes insufficient on one hand and thecorrection of aberrations becomes difficult on the other hand.

Furthermore, with the increase of the zoom-ratio, the assembling errorsuch as tilt of each lens or each lens group during the assembling willincrease. If the sensitivity by decentration of the lens and lens groupis large, the optical performance degrades largely with the decentrationand this causes considerable deterioration of the optical performanceduring the vibration control. In consideration of this, in the zoom lensthe sensitivity by decentration of each lens and each lens group shouldbe made as small as possible.

In the zoom lens of Japanese Laid-Open Patent Application No. 10-232420,the first lens group and the third lens group are fixed relative to theimage plane during the zooming. Thus, as compared with the configurationin which the first lens group moves to perform the variation change, thefront lens diameter and the lens overall length have to be made larger.If the refracting power of each lens group is made larger (stronger) forreduction in size of the whole system, the sensitivity by decentrationbecomes larger. This causes degradation of the optical performance dueto production errors or degradation of optical performance during thevibration control. It is very difficult to correct these.

In the zoom lens of U.S. Pat. No. 6,266,189, all lens groups are movedfor the zooming. Also, the third lens group is comprised of a fore groupof positive refracting power and a rear group of negative refractingpower. The fore group is moved in a direction perpendicular to theoptical axis to perform the vibration control. The fore group iscomprised of a single piece of lens, and the rear group is comprised ofthree pieces of lenses.

In U.S. Pat. No. 6,266,189, if the movement amount of the fore group inthe perpendicular direction during the vibration control is to be madesmall while assuring higher zoom ratio, the refracting power of the foregroup has to be made large. Since the fore group is comprised of asingle piece of lens, mainly the correction of spherical aberration orcomatic aberration becomes difficult. If to the contrary the positiverefracting power of the fore group is made weak, the movement amount inthe perpendicular direction during the vibration control becomes large.As a result, the effective diameter of the third lens group increaseswhich makes the compactification difficult. Furthermore, deteriorationof the optical performance by decentration becomes quite large.

Furthermore, if the number of lenses of the fore group is increased tocompensate the deterioration of the optical performance during thevibration control, the total lens number of the third lens groupincreases, which makes the compactification difficult.

In the four-group zoom lens and five-group zoom lens described above, inorder to obtain good optical performance while assuring a high zoomratio and reduction in size of the whole lens system, it is veryimportant to set the refracting power and the lens structure of eachlens group as well as the movement condition during the zooming of eachlens group appropriately.

Particularly, in order to assure smaller decentration aberration andgood optical performance during the vibration control, it is veryimportant to set the lens structure and the like of the third lens groupincluding a vibration control lens group appropriately.

If these structures are not suitably set, it becomes very difficult tomaintain high optical performance during the vibration control whilesecuring a high zoom ratio.

SUMMARY OF THE INVENTION

The present invention provides a zoom lens and/or an image pickupapparatus having the same by which at least one of the inconveniencesmentioned above can be removed or reduced.

In accordance with an aspect of the present invention, there is provideda zoom lens comprising: a first lens group of positive refracting power;a second lens group of negative refracting power; a third lens group ofpositive refracting power; and a fourth lens group of positiverefracting power, wherein said first to fourth lens groups are providedin this order from an object side to an image side, wherein, duringzooming from a wide-angle end to a telephoto end, at least said firstlens group moves, wherein said third lens group includes, in an orderfrom the object side to the image side, a first lens sub-group ofpositive refracting power and a second lens sub-group of negativerefracting power, wherein said second lens sub-group of said third lensgroup is comprised of a single negative lens, wherein said first lenssub-group of said third lens group is moved to keep a perpendicularcomponent relative to an optical axis to correct image blur to beproduced when said zoom lens vibrates, and wherein, when a focal lengthof said first lens group is denoted by f1 and a the focal length of thewhole system at the wide-angle end is denoted by fw, a conditionalexpression10.0<f1/fw<20.0is satisfied.

When a focal length of said first lens sub-group of said third lensgroup is denoted by f3 a and a focal length of said fourth lens group isdenoted by f4, a conditional expression0.3<f3a/f4<0.8is satisfied

When a focal length of said first lens sub-group of said third lensgroup is denoted by f3 a and a focal length of said second lenssub-group of said third lens group is denoted by f3 b, a conditionalexpression−0.6<f3a/f3b<−0.1is satisfied

When focal lengths of said first and third lens groups are denoted by f1and f3, a conditional expression2.5<f1/f3<4.5is satisfied.

When focal lengths of said third and fourth lens groups are denoted byf3 and f4, a conditional expression0.2<f3/f4<1.0is satisfied.

When the focal length of the whole system at the wide-angle end and thetelephoto end is denoted by fw and ft, respectively, a conditionalexpression18.0<ft/fw<40.0is satisfied.

The first lens sub-group of said third lens group includes at least twopieces of positive lenses and one piece of negative lens.

The first lens group is comprised of three lenses which are, in an orderfrom the object side to the image side, a negative lens, a positive lensand a positive lens.

The second lens group is comprised of four lenses which are, in an orderfrom the object side to the image side, a negative lens, a negativelens, a negative lens and a positive lens.

The second lens sub-group of said third lens group is comprised of asingle negative lens having a meniscus shape.

The fourth lens group is comprised of one piece of positive lens or acemented lens having a positive lens and a negative lens cemented toeach other.

The zoom lens may further comprise a fifth lens group of positiverefracting power provided at the image side of said fourth lens group,wherein said fifth said lens group is held stationary during thezooming.

The first lens sub-group of said third lens group is comprised of, in anorder from the object side to the image side, a positive lens, anegative lens with a surface of concave shape at the image side, and apositive lens.

The first lens sub-group of said third lens group is comprised of, in anorder from the object side to the image side, a positive lens, anegative lens with a surface of concave shape at the image side, and acemented lens having a positive lens and a negative lens cemented toeach other.

In accordance with another aspect of the present invention, there isprovided an image pickup apparatus comprising: a zoom lens as recitedabove; and a solid-state image pickup device configured to receive animage formed by said zoom lens.

In summary, the present invention provides a zoom lens with a vibrationcontrol function by which the whole optical system can be made small insize and, yet, a good pictorial image can be maintained during thevibration compensation.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a zoom lens at the wide-angle end,according to a first embodiment of the present invention.

FIG. 2A through FIG. 2C are aberration diagrams of numerical example 1corresponding to the first embodiment of the present invention.

FIG. 3 is a sectional view of a zoom lens at the wide-angle end,according to a second embodiment of the present invention.

FIG. 4A through FIG. 4C are aberration diagrams of numerical example 2corresponding to the second embodiment of the present invention.

FIG. 5 is a sectional view of a zoom lens at the wide-angle end,according to a third embodiment of the present invention.

FIG. 6A through FIG. 6C are aberration diagrams of numerical example 4corresponding to the third embodiment of the present invention.

FIG. 7 is a sectional view of a zoom lens at the wide-angle end,according to a fourth embodiment of the present invention.

FIG. 8A through FIG. 8C are aberration diagrams of numerical example 4corresponding to the fourth embodiment of the present invention.

FIG. 9 is a sectional view of a zoom lens at the wide-angle end,according to a fifth embodiment of the present invention.

FIG. 10A through FIG. 10C are aberration diagrams of numerical example 5corresponding to the fifth embodiment of the present invention.

FIG. 11 is a sectional view of a zoom lens at the wide-angle end,according to a sixth embodiment of the present invention.

FIG. 12A through FIG. 12C are aberration diagrams of numerical example 6corresponding to the sixth embodiment of the present invention.

FIG. 13 is a schematic diagram of an image pickup apparatus according tothe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of zoom lens and image pickup apparatus having thesame according to the present invention will now be described withreference to the attached drawings.

A zoom lens of the present invention comprises, in an order from theobject side to the image side, a first lens group of positive refractingpower, a second lens group of negative refracting power, a third lensgroup of positive refracting power, and a fourth lens group of positiverefracting power.

There may be a fifth lens group of positive refracting power at theimage side of the fourth lens group.

The zoom lens is configured so that, for the zooming from the wide-angleend to the telephoto end, at least the first lens group moves.

In the embodiments to be described below, first to fourth lens groupsmove. The third lens group is comprised of, in an order from the objectside to the image side, a “3 a-th” lens group L3 a of positiverefracting power for vibration control and a “3 b-th” lens group L3 b ofnegative refracting power. The “3 b-th” lens group L3 b is comprised ofa single negative lens.

The “3 a-th” lens group L3 a is moved so as to keep a perpendicularcomponent relative to the optical axis to shift the pictorial image in adirection perpendicular to the optical axis. This is done to correct theblurring of the pictorial image.

FIG. 1 is a sectional view of a zoom lens at the wide-angle end (shortfocal-length end), according to a first embodiment of the presentinvention. FIG. 2A, FIG. 2B and FIG. 2C are aberration diagrams of thezoom lens of the first embodiment at the wide-angle end, theintermediate zooming position and the telephoto end (long focal-lengthend), respectively.

FIG. 3 is a sectional view of a zoom lens at the wide-angle end,according to a second embodiment of the present invention. FIG. 4A, FIG.4B and FIG. 4C are aberration diagrams of the zoom lens of the secondembodiment at the wide-angle end, the intermediate zooming position andthe telephoto end, respectively.

FIG. 5 is a sectional view of a zoom lens at the wide-angle end,according to a third embodiment of the present invention. FIG. 6A, FIG.6B and FIG. 6C are aberration diagrams of the zoom lens of the secondembodiment at the wide-angle end, the intermediate zooming position andthe telephoto end, respectively.

FIG. 7 is a sectional view of a zoom lens at the wide-angle end,according to a fourth embodiment of the present invention. FIG. 8A, FIG.8B and FIG. 8C are aberration diagrams of the zoom lens of the fourthembodiment at the wide-angle end, the intermediate zooming position andthe telephoto end, respectively.

FIG. 9 is a sectional view of a zoom lens at the wide-angle end,according to a fifth embodiment of the present invention. FIG. 10A, FIG.10B and FIG. 10C are aberration diagrams of the zoom lens of the fifthembodiment at the wide-angle end, the intermediate zooming position andthe telephoto end, respectively.

FIG. 11 is a sectional view of a zoom lens at the wide-angle end,according to a sixth embodiment of the present invention. FIG. 12A, FIG.12B and FIG. 12C are aberration diagrams of the zoom lens of the sixthembodiment at the wide-angle end, the intermediate zooming position andthe telephoto end, respectively.

FIG. 13 is a schematic diagram of a main portion of a camera (imagepickup apparatus) having a zoom lens according to the present invention.

The zoom lenses of these embodiments are a photographic lens systemwhich can be used in an image pickup apparatus such as a video camera,digital camera or silver film camera. In the lens sectional diagrams,the left-hand side corresponds to the photogenic subject side (objectside) (front), and the right-hand side corresponds to the image side(rear). Also, in the lens sectional diagrams, the reference character“i” denotes the order (ordinal) of the lens group counted from theobject side, and “Li” denotes the i-th lens group.

In the lens sectional diagrams of FIG. 1, FIG. 3, FIG. 5, FIG. 7 andFIG. 11 according to the first to fourth and sixth embodiments,respectively, L1 denotes a first lens group of positive refracting power(optical power=the reciprocal of the focal length), L2 denotes a secondlens group of negative refracting power, L3 denotes a third lens groupof positive refracting power, and L4 denotes a fourth lens group ofpositive refracting power. Thus, the first to fourth and sixthembodiments concern a four-group zoom lens.

In the lens sectional diagram of FIG. 9 corresponding to the fifthembodiment of the present invention, L1 denotes a first lens group ofpositive refracting power, L2 denotes a second lens group of negativerefracting power, L3 denotes a third lens group of positive refractingpower, L4 denotes a fourth lens group of positive refracting power, andL5 denotes a fifth lens group of positive refracting power. Thus, thefifth embodiment concerns a five-group zoom lens.

In these embodiments, the third lens group L3 is comprised of, in anorder from the object side to the image side, a “3 a-th” lens group L3 aof positive refracting power and a “3 b-th” lens group L3 b of negativerefracting power. The “3 b-th” lens group L3 b is comprised of a singlenegative lens.

Denoted at SP is an aperture stop which is disposed at the object sideof the third lens group L3. Denoted in FIG. 1, FIG. 3, FIG. 5, FIG. 7,FIG. 9 and FIG. 11 at FP is a flare stop which is disposed at the imageside of the third lens group L3. The flare stop is configured to blockunwanted light.

Denoted at G is an optics block which is equivalent to an opticalfilter, a face plate, a crystal low-pass filter or an infrared cut-offfilter, for example.

Denoted at IP is an image plane. When the zoon lens is used as aphotography optical system in a video camera or a digital still camera,the image plane is at the image pickup surface of a solid-state imagepickup device (photoelectric converting element) such as a CCD sensor orCMOS sensor. When the zoon lens is used in a silver film camera, thephotosensitive surface corresponding to the film surface is placedthere.

In the aberration diagrams, reference characters d and g denote thed-line and g-line, respectively. Reference characters ΔM and ΔS denotethe meridional image plane and the sagittal image plane, respectively.The chromatic aberration of magnification is depicted in terms of theg-line. Reference character ω denotes the half field angle (a half valueof the photographic field angle), and fno denotes the F number.

It should be noted that, in the following embodiments, the wide-angleend and the telephoto end refer to the zoom positions when the powerchanging lens group is located at the opposite ends of the mechanicallymovable range on the optical axis, respectively.

In the following embodiments, the first to fourth lens groups L1-L4 aremoved as depicted by arrows during the zooming from the wide-angle endto the telephoto end.

More specifically, in these embodiments, during the zooming from thewide-angle end to the telephoto end, the first lens group L1 is moved asdepicted by an arrow so as to define a locus which is being convexedtoward the image side. The second lens group L2 is moved nonlinearly tothe image side. The third lens group L3 is moved to an object side. Thefourth lens group L4 is moved so as to define a locus which is beingconvexed toward the object side.

In the fifth embodiment of FIG. 9, the fifth lens group L5 is heldstationary during the zooming. It should be noted that, if necessary,the fifth lens group L5 may be moved independently from the other lensgroups.

In these embodiments, during the zooming, the first lens group L1 andthe third lens group L3 are so moved that, as compared with thewide-angle end, at the telephoto end both of the first and third lensgroups are located at the object side. With this arrangement, a largepower changing ratio can be provided while assuring a shortened lensoverall length at the wide-angle end.

Particularly, in these embodiments, during the zooming the third lensgroup L3 is moved toward the object side, such that the third lens groupL3 shares the power changing function. Furthermore, the first lens groupL1 of positive refracting power is moved toward the object side. Bydoing so, the second lens group L2 can have a large power changingeffect. Thus, a large zooming ratio of 18× or more is obtainable withoutenlarging the refracting power of second lens group L2 too much.

Furthermore, the rear focus type structure in which the fourth lensgroup L4 is moved along the optical axis to perform the focusing isadopted.

When at the telephoto end the focusing is to be carried out from aninfinity object to a short-distance object, the fourth lens group L4 ismoved forwardly as shown by an arrow 4 c in FIG. 1. A solid line curve 4a and a broken-line curve 4 b concerning the fourth lens group L4 depictthe movement loci for correcting the image plane change caused by thezooming from the wide-angle end to the telephoto end when the lens isfocused on an infinity object and a short distance object, respectively.

Furthermore, the “3 a-th” lens group L3 a having a positive refractingpower is moved to keep a perpendicular component relative to the opticalaxis so as to shift the image in the direction perpendicular to theoptical axis. By this, the blurring of the photographic image when theoptical system (zoom lens) as a whole vibrates (tilts) is corrected.

In these embodiments, the vibration control is performed without addingan optical member such as a variable vertex-angle prism or a vibrationcontrol lens group. This avoids enlargement in size of the whole opticalsystem.

It should be noted that, although in these embodiments the vibrationcontrol is performed by moving the “3 a-th” lens group L3 a is moved ina direction perpendicular to the optical axis, the moving method is notlimited to this. As long as the lens group L3 a is moved to keep aperpendicular component relative to the optical axis, it is possible tocorrect the image blur. For example, if some complexity of the lensbarrel structure is allowed, the vibration control may be performed bypivotally moving the “3 a-th” lens group L3 a so that the pivot centeris placed on the optical axis.

Furthermore, in these embodiments, during the zooming the aperture stopSP moves independently of the lens groups. With this arrangement, asteep drop of the light quantity occurring from an intermediate imageheight to the circumferential portion of the image plane at thewide-angle end and an adjacent zooming position can be improved.

In order to make small the effective lens diameter of the first lensgroup L1, the number of lenses constituting the first lens group L1should preferably be small. The first lens group L1 is comprised ofthree lenses which are, in an order from the object side to the imageside, a negative lens, a positive lens and a positive lens.

More specifically, in these embodiments, the first lens group L1 isprovided by a cemented lens having a single positive lens and a singlenegative lens cemented to each other, and a positive lens.

With this structure, spherical aberration and chromatic aberration to becaused by enlarging the zoom ratio is well corrected.

The second lens group L2 comprises four lenses which are a negativelens, a negative lens, a negative lens and a positive lens. Morespecifically, it is comprised of four independent lenses: a negativelens of meniscus shape having a convex surface at the object side, anegative lens of meniscus shape having a convex shape at the objectside, a negative lens of biconcave shape, and a positive lens having aconvex shape at the object side.

With this arrangement, the variation of aberration during the zooming isreduced, and distortion at the wide-angle end and spherical aberrationat the telephoto end are well corrected.

In these embodiments, the third lens group of positive refracting powerL3 is divided into a “3 a-th” lens group L3 a of positive refractingpower and a “3 b-th” lens group L3 b of negative refracting power. Also,the positive refracting power of the “3 a-th” lens group L3 a isenlarged to compensate use of the “3 b-th” lens group L3 b having anegative refracting power. By doing so, the decentration sensitivity ofthe “3 a-th” lens group L3 a is magnified, such that a zoom lens with acompact optical system is realized.

The “3 a-th” lens group L3 a includes at least two pieces of positivelenses and one piece of negative lens.

Specifically, the “3 a-th” lens group L3 a comprises, in an order fromthe object side to the image side, a positive lens, a negative lens witha concave surface at the image plane side, and a positive lens.Alternatively, it may comprise a positive lens, a negative lens with aconcave surface at the image plane side, and a cemented lens having anegative lens and a positive lens cemented to each other.

With this arrangement, mainly the spherical aberration and comaticaberration at the telephoto end are well corrected. Furthermore, duringthe vibration control, the quantity of decentration aberration generatedis reduced, and good optical performance during the vibration control ismaintained.

The “3 b-th” lens group L3 b is comprised of a single negative lens ofmeniscus shape. The “3 b-th” lens group L3 b functions to improve thecorrection of curvature of field in an intermediate power changing zone(intermediate zooming region) as well as the vibration controlsensitivity (which can be defined as the movement amount of the imageplane in the perpendicular direction when the vibration control lensgroup moves by 1 mm in a direction perpendicular to the optical axis) ofthe “3 a-th” lens group L3 a. Also, at the same time, it contributes tothe improvement of the focus sensitivity (which can be defined as themovement amount of the image plane in the optical axis direction whenthe focusing lens group moves by 1 mm in the optical axis direction) ofthe fourth lens group L4. With this arrangement, compactification(reduction in size) of the third lens group L3 as well as simplificationof the structure are assured. Furthermore, the focus movement amount ofthe fourth lens group L4 throughout the whole object distance isshortened, such that reduction in size of the lens barrel is enabled.

The third lens group L3 has one or more aspherical surfaces. This iseffective to well correct the aberration change with the zooming.

The fourth lens group L4 is comprised of a single positive lens having aconvex surface at the object side or, alternatively, a cemented lenshaving a positive lens and a negative lens cemented to each other.

In the fifth embodiment of FIG. 9, a fifth lens group L5 of positiverefracting power which is held stationary (immovable) relative to theimage plane during the zooming, is disposed closest to the image planeside. It contributes to correction of aberrations such as the curvatureof field, reduction in size of the front lens diameter and the powerchange.

The zoom lens according to these embodiments includes at least four lensgroups which are, in an order from the object side to the image side, afirst lens group L1 of positive refracting power, a second lens group L2of negative refracting power, a third lens group L3 of positiverefracting power, and a fourth lens group L4 of positive refractingpower.

During the zooming (power change) from the wide-angle end to thetelephoto end, at least the first lens group is moved. Then, the thirdlens group L3 is constituted by, in an order from the object side to theimage side, a “3 a-th” lens group of positive refracting power and a “3b-th” lens group of negative refracting power. The “3 b-th” lens groupis comprised of a single negative lens. The “3 a-th” lens group L3 a ismoved to keep a perpendicular component relative to the optical axis, bywhich the blurring of the pictorial image as the zoom lens vibrates iscorrected.

By changing the power by moving the first lens group L1, the lensoverall length at the wide-angle end can be shortened, and the frontlens diameter can be reduced as well. Thus, overall compactification isenabled. Furthermore, the vibration control is performed by means of the“3 a-th” lens group L3 a of the third lens group L3, having a relativelystrong positive refracting power. With this arrangement, the movementamount in the perpendicular direction can be made smaller than a casewhere, as an example, the vibration control is carried out by means ofthe “3 b-th” lens group L3 b. Thus, the effective diameter of the lensesconstituting the third lens group L3 and the size of the vibrationcontrol unit can be made smaller. Furthermore, the weight can be lightedas compared with an example wherein the vibration control is carried outby using the third lens group L3 as a whole. Also, the vibration controlsensitivity of the “3 a-th” lens group L3 a and the focus sensitivity ofthe fourth lens group L4 are improved based on the “3 b-th” lens groupL3 b of negative refracting power.

With this structure, the shortening of the movement amount of the “3a-th” lens group L3 a in the perpendicular direction during thevibration control as well as the shortening of the focusing stroke ofthe fourth lens group L4 during the focusing are assured.

Furthermore, the “3 b-th” lens group L3 b is constituted by a singlenegative lens. By this, the barrel structure of the third lens group L3is simplified and the thickness of the third lens group L3 in theoptical axis direction can be reduced. Thus, reduction in size isenabled. Moreover, the “3 b-th” lens group L3 b which is a singlenegative lens performs correction of the field curvature, due to themovement of each lens group, throughout the whole zoom region. If, forexample, the “3 b-th” lens group L3 b is constituted by a cemented lensor the like having a positive lens and a negative lens cemented to eachother, it results in that not only the size of the lens group in thethickness direction increases but also correction of the chromaticaberration and correction of the curvature of field are difficult toachieve at the same time. If the chromatic aberration is corrected, thefield curvature particularly in the intermediate zooming region turnsworse.

When the focal length of the first lens group L1 is denoted by f1 andthe focal length of the whole system at the wide-angle end is denoted byfw, conditional expression (1) below is satisfied.10.0<f1/fw<20.0  (1)

Conditional expression (1) appropriately defines the ratio between thefocal length f1 of the first lens group L1 which contributes to thepower changing and the focal length fw of the whole system at thewide-angle end.

If the focal length f1 of the first lens group L1 becomes shorter thanthe lower limit of conditional expression (1), mainly at the telephotoend the longitudinal chromatic aberration, chromatic aberration ofmagnification, spherical aberration and so on turn worse. Additionally,it becomes difficult to secure the thickness of the periphery of thepositive lens constituting the first lens group L1. Therefore, the lensoutside diameter has to be enlarged for the purpose of production. Thisis not preferable.

If to the contrary the focal length f1 of the first lens group L1becomes longer than the upper limit of conditional expression (1), themovement amount of the first lens group L1 during the zooming becomeslarge, and thus the lens overall compactification is difficult to do.Furthermore, with the increase of the movement amount, image jogglingduring the zooming or vibration sound will be generated. This is notpreferable.

More preferably, the numeral range of conditional expression (1) hadbetter be set as follows.10.0<f1/fw<18.0  (1a)

With the above-described configuration of these embodiments, the amountof decentration aberration caused when the lens group is decentered soas to correct the blurring of the pictorial image can be made small.Thus, a zoom lens and an image pickup apparatus (optical instrument)having the same by which the vibration control can be well carried outwhile maintaining high optical performance, are achieved.

Particularly, some lens group constituting the zoom lens is moved tokeep the perpendicular component relative to the optical axis. With thisarrangement, a zoom lens suitable for a digital camera, a video camera,an electronic still camera or a silversalt photographic camera in whichstabilization of the captured image as the zoom lens vibrates (tilts),is accomplished.

In accordance with the embodiments described above, a small-size zoomlens having high zoom ratio and providing good optical performancethroughout the whole zooming region, is accomplished.

In the present invention, more preferably, one or more of the followingconditions had better be satisfied.

The focal lengths of the first, second, third and fourth lens groups L1,L2, L3 and L4 are denoted by f1, f2, f3 and f4, respectively. The focallengths of the whole system at the wide-angle end and the telephoto endare denoted by fw and ft, respectively.

The focal lengths of the “3 a-th” lens group and the “3 b-th” lens groupare denoted by f3 a and f3 b, respectively.

Here, at least one of the following conditional expressions had betterbe satisfied.0.3<f3a/f4<0.8  (2)−0.6<f3a/f3b<−0.1  (3)2.5<f1/f3<4.5  (4)0.2<f3/f4<1.0  (5)18.0<ft/fw<40.0  (6)

Next, the technical meaning of these conditional expressions will beexplained.

Conditional expression (2) is a condition for appropriately setting theratio between the focal length f3 a of the “3 a-th” lens group L3 aconstituting the third lens group L3 which contributes to the powerchanging and the focal length f4 of the fourth lens group L4, so as toassure a high zooming ratio while reducing the size of the whole system.

If the focal length f3 a of the “3 a-th” lens group L3 a becomes shorterthan the lower limit of conditional expression (2), the power(refracting power) of the fourth lens group L4 becomes weak, and themovement amount of the fourth lens group L4 during the zooming andfocusing becomes large. Thus, the lens overall length increases, and itis not preferable. Furthermore, since the refracting power of the “3a-th” lens group L3 a becomes large, mainly correction of sphericalaberration and comatic aberration becomes difficult to do. Also, sincethe decentration sensitivity of the “3 a-th” lens group L3 a becomeshigher, correction of aberrations such as comatic aberration orcurvature of field during the vibration control becomes difficult toachieve. Further, the required central positioning accuracy of the “3a-th” lens group L3 a during the vibration control becomes very strict,causing a difficulty in the production.

If to the contrary the focal length f3 a of the “3 a-th” lens group L3 abecomes longer than the upper limit of conditional expression (2), thesharing proportion of power changing of the “3 a-th” lens group L3 abecomes small, and thus increasing the zooming ratio is difficult toachieve. Furthermore, the movement amount in the direction perpendicularto the optical axis during the vibration control becomes large, whichcauses an increase of the lens diameter of the third lens group L3. Thisis not preferable.

Conditional expression (3) is a condition for appropriately setting theratio between the focal length f3 a of the “3 a-th” lens group L3 a andthe focal length f3 b of the “3 b-th” lens group L3 b so as to achievecompactification of the third lens group L3 as a whole.

If the focal length f3 a of the “3 a-th” lens group L3 a becomes shorterthan the lower limit of conditional expression (3), mainly thecorrection of spherical aberration or comatic aberration becomesdifficult to achieve. Furthermore, since the decentration sensitivity ofthe “3 a-th” lens group L3 a becomes higher, the optical performanceduring the vibration control turns worse. Moreover, the required centralpositioning accuracy of the “3 a-th” lens group L3 a during thevibration control becomes very strict, causing a difficulty in theproduction.

If to the contrary the focal length f3 b of the “3 b-th” lens group L3 bbecomes longer than the upper limit of conditional expression (3), itbecomes difficult to improve the vibration control sensitivity of the “3a-th” lens group L3 a. Furthermore, throughout the whole zooming region,mainly the correction of curvature of field and comatic aberrationbecomes difficult to attain.

Conditional expression (4) is a condition for appropriately setting theratio between the focal length f1 of the first lens group L1,contributable to the power changing, and the focal length f3 of thethird lens group L3 so as to achieve a high zooming ration while keepingthe whole system compact.

If the focal length f1 of the first lens group L1 becomes shorter thanthe lower limit of conditional expression (4), mainly the longitudinalchromatic aberration at the telephoto end as well as the chromaticaberration of magnification and spherical aberration turn worse.Furthermore, it becomes difficult to secure the thickness of theperiphery of the positive lens constituting the first lens group L1. Asa result, the lens outside diameter has to be made large, and this isnot preferable.

Furthermore, if the focal length f3 of third lens group L3 becomes long,mainly the correction of spherical aberration and comatic aberrationbecomes difficult to achieve.

If to the contrary the focal length f1 of the first lens group L1becomes longer than the upper limit of conditional expression (4), themovement amount of the first lens group L1 during the zooming becomeslarge, causing a difficulty in compactification of the lens wholesystem. Furthermore, with the increase of the movement amount, imagejoggling during the zooming or vibration sound is generated. This is notpreferable. On the other hand, if the focal length f3 of the third lensgroup L3 becomes short, the incidence angle of the light beam enteringthe fourth lens group L4 becomes large. As a result, the opticalperformance changes largely when the focusing is carried out by thefourth lens group L4. Furthermore, the sensitivity to decentration ofthe third lens group L3 becomes large, causing a difficulty in theproduction or assembly.

Conditional expression (5) is a condition for appropriately setting theratio between the focal length f3 of the third lens group L3 and thefocal length f4 of the fourth lens group L1 so as to achieve a highzooming ration while keeping the whole system compact.

If the focal length f3 of the third lens group L3 becomes shorter thanthe lower limit of conditional expression (5), the refracting power ofthe fourth lens group L4 becomes relatively weak, and the stroke of thefourth lens group L4 with the focusing becomes large particularly at thetelephoto end. Thus, the lens overall length increases, and it is notpreferable.

Furthermore, since the refracting power of the third lens group L3becomes large, mainly the correction of spherical aberration and comaticaberration becomes difficult.

If on the other hand the focal length f3 of the third lens group L3becomes short, mainly the change of the incidence angle of the lightbeam entering the fourth lens group L4 when the same is focused at thetelephoto end becomes large. It results in a large change of the opticalperformance due to the change in the object distance, and this is notpreferable.

If to the contrary the focal length f3 of the third lens group L3becomes longer than the upper limit of conditional expression (5), thesharing proportion of the power change of the third lens group L3becomes small, and thus increasing the zooming ratio becomes difficult.Also, mainly the correction of spherical aberration and comaticaberration becomes difficult to achieve. Furthermore, if the focallength f4 of the fourth lens group L4 becomes short, the light beamincident on the imaging plane changes largely with the zooming, causingcolor shading. This is not preferable.

Conditional expression (6) is a condition concerning the zooming ratioand for assuring effective vibration control when the third lens groupL3 is divided into a positive “3 a-th” lens group L3 a and a negative “3b-th” lens group L3 b and the vibration control is performed based onthe positive “3 a-th” lens group L3 a.

If the focal length ft goes beyond the lower limit of conditionalexpression (6) and becomes smaller than the focal length fw (i.e., ifthe zoom ratio becomes too small), during the vibration control themovement amount of the “3 a-th” lens group L3 a in the perpendiculardirection becomes small. As a result, the difference with the effect ofvibration control when the same is done based on the third lens group L3as a whole becomes small. This is not preferable.

If to the contrary the focal length ft goes beyond the upper limit ofconditional expression (6) and becomes larger than the focal length fw(i.e., if the zoom ratio becomes too large), during the vibrationcontrol the movement amount of the “3 a-th” lens group L3 a in theperpendicular direction becomes large. This causes quite largedeterioration of the optical performance during the vibration control,and this is not preferable.

It should be noted that, in each of these embodiments, for betteraberration correction and for further reduction in size of the lenswhole system while suppressing the aberration change during the zooming,the numerical ranges of conditional expressions (1) to (6) had better beset as follows.0.35<f3a/f4<0.70  (2a)−0.55<f3a/f3b<−0.15  (3a)2.7<f1/f3<4.2  (4a)0.30<f3/f4<0.85  (5a)18.5<ft/fw<35.0  (6a)

In accordance with these embodiments as described hereinbefore, in orderto correct the blurring of the pictorial image, the third lens group L3is suitably divided into two lens groups and the power distribution ofthese lens groups is set appropriately. With this arrangement, a zoomlens in which the amount of decentration aberration to be caused by thedecentration is well suppressed and high optical performance isaccomplished is provided. Particularly, with the present invention, goodoptical performance during the vibration control at the telephoto endcan be maintained.

Next, numerical examples 1-6 corresponding to the first to sixthembodiments of the present invention will be explained. In thesenumerical examples, the reference character “I” denotes the order(ordinal) of the optical surface counted from the object side. Also,“ri” denotes the curvature radius of the i-th optical surface (i-thsurface), and “di” denotes the spacing between the i-th surface and(i+1)th surface. Furthermore, “ndi” and “vdi” denote the refractiveindex of material of the i-th optical member with respect to the d-lineand the Abbe's number, respectively.

Furthermore, “k” denotes the eccentricity, and “A4”, “A6”, “A8” and“A10” denote aspherical coefficients, respectively. When thedisplacement in the optical axis direction at a position of the height hfrom the optical axis is denoted by x while taking the plane vertex as areference, the aspherical shape can be represented by the followingequation.x=(h2/R)/[1+[1-(1+k)(h/R)2]1/2]+A4h4+A6h6+A8h8+A10h10where R is the paraxial curvature radius. Also, the expression of “E-Z”means “10-Z”.

In the numerical examples, the last two surfaces are the surfaces of anoptics block such as a filter, a face plate and the like.

In each of these embodiments, the back focus (BF) represents thedistance from the lens final surface to the paraxial image plane, interms of the air converted length. The lens overall length correspondsto the distance from the plane closes to the object side to finalsurface plus the back focus. Also, “d28” of numerical examples 1-4 and“d28” of numerical examples 5 and 6 are the distance up to the imageplane.

Also, Table 1 shows the correspondence with the conditional expressionsin each numerical example.

NUMERICAL EXAMPLE 1

Surface Data Surface No. r d nd νd  1 76.150 1.80 1.80610 33.3  2 37.3206.30 1.49700 81.5  3 −839.796 0.20  4 36.109 4.25 1.60311 60.6  5156.842 (variable)  6 54.202 1.00 1.88300 40.8  7 11.015 2.10  8 28.0900.80 1.88300 40.8  9 9.248 3.60 10 −27.934 0.70 1.80610 33.3 11 64.0070.20 12 20.074 2.40 1.92286 18.9 13 −96.663 (variable) 14 (stop)infinite (variable) 15* 10.150 3.20 1.58313 59.4 16 −62.532 2.82 1730.340 0.80 1.80610 33.3 18 10.076 0.50 19 18.258 0.70 2.00069 25.5 208.638 2.70 1.71999 50.2 21 −35.972 0.50 22 86.235 0.70 1.58313 59.4 2330.000 0.30 24 (FP) infinite (variable) 25* 20.173 2.00 1.58313 59.4 26388.237 (variable) 27 infinite 1.00 1.51633 64.1 28 infinite AsphericalSurface Data 15t Surface K = −5.09950e−001, A4 = −6.19890e−005, A6 =4.89106e−007, A8 = −6.83395e−008, A10 = 2.12024e−009 25th Surface K =−2.71019e+000, A4 = 3.64245e−005, A6 = 3.16922e−007, A8 = −6.60093e−009Various Data Zoom Ratio: 19.08 Wide Intermediate Telephoto Focal Length5.13 17.56 97.76 F number 2.87 3.59 5.84 Field Angle 37.09 12.45 2.27Image Height 3.88 3.88 3.88 Total Lens Length 87.05 92.42 119.09 BF10.07 17.02 9.34 d5 0.70 21.82 41.22 d13 26.46 8.88 2.04 d14 7.79 3.751.10 d24 4.46 3.39 27.82 d26 8.41 15.36 7.68 d28 1.00 1.00 1.00 ZoomLens Group Data Group Initial Surface Focal Length 1 1 63.49 2 6 −9.38 315 19.45 4 25 36.42

NUMERICAL EXAMPLE 2

Surface Data Surface No. r d nd νd  1 86.433 1.80 1.80610 33.3  2 41.6926.25 1.49700 81.5  3 −480.535 0.20  4 37.627 4.10 1.60311 60.6  5126.596 (variable)  6 43.256 1.00 1.88300 40.8  7 10.771 2.10  8 31.0810.80 1.88300 40.8  9 9.486 3.60 10 −28.214 0.70 1.80610 33.3 11 107.4460.20 12 20.755 2.40 1.92286 18.9 13 −121.587 (variable) 14 (stop)infinite (variable) 15* 9.768 3.20 1.58313 59.4 16 −53.234 2.73 1736.132 0.70 1.80610 33.3 18 9.566 0.50 19 17.292 0.70 2.00069 25.5 208.781 2.70 1.71999 50.2 21 −31.232 0.40 22 −203.125 0.70 1.69680 55.5 2361.553 0.30 24 (FP) infinite (variable) 25 20.699 1.80 1.58313 59.4 26187.324 (variable) 27 infinite 1.00 1.51633 64.1 28 infinite AsphericalSurface Data 15th Surface K = −4.50746e−001, A4 = −7.56392e−005, A6 =6.03037e−007, A8 = −7.75261e−008, A10 = 2.12024e−009 Various Data ZoomRatio: 19.07 Wide Intermediate Telephoto Focal Length 5.12 14.48 97.73 Fnumber 2.83 3.52 5.87 Field Angle 37.09 14.98 2.27 Image Height 3.883.88 3.88 Total Lens Length 87.50 93.61 124.13 BF 10.07 15.26 10.24 d50.70 20.73 45.71 d13 27.52 12.08 1.96 d14 7.85 3.81 1.10 d24 4.48 4.8528.23 d26 8.41 13.60 8.58 d28 1.00 1.00 1.00 Zoom Lens Group Data GroupInitial Surface Focal Length 1 1 70.00 2 6 −9.80 3 15 19.27 4 25 39.75

NUMERICAL EXAMPLE 3

Surface Data Surface No. r d nd νd  1 67.094 1.80 1.80610 33.3  2 31.6836.25 1.49700 81.5  3 −370.584 0.20  4 29.958 4.10 1.60311 60.6  5132.718 (variable)  6 74.017 1.00 1.88300 40.8  7 11.680 2.10  8 28.7020.80 1.88300 40.8  9 8.086 3.60 10 −22.265 0.70 1.80610 33.3 11 65.8690.20 12 19.756 2.40 1.92286 18.9 13 −66.184 (variable) 14 (stop)infinite (variable) 15* 8.855 3.20 1.58313 59.4 16 −21.744 2.74 1771.030 0.70 1.80610 33.3 18 8.465 0.50 19 14.132 0.70 2.00069 25.5 207.007 2.70 1.71999 50.2 21 −29.089 0.40 22 −68.175 0.70 1.69680 55.5 2334.073 0.30 24 (FP) infinite (variable) 25 15.607 1.80 1.58313 59.4 26−1661.846 (variable) 27 infinite 1.00 1.51633 64.1 28 infiniteAspherical Surface Data 15th Surface K = −7.52773e−001, A4 =−1.16164e−004, A6 = 4.08440e−007, A8 = −8.49947e−008, A10 = 2.12024e−009Various Data Zoom Ratio: 19.03 Wide Intermediate Telephoto Focal Length5.12 16.26 97.51 F number 2.87 3.57 5.88 Field Angle 37.09 13.40 2.28Image Height 3.88 3.88 3.88 Total Lens Length 78.71 83.00 103.94 BF 8.1414.45 6.72 d5 0.70 17.17 33.58 d13 20.75 7.38 1.99 d14 7.85 3.95 1.09d24 4.38 3.15 23.66 d26 6.48 12.79 5.06 d28 1.00 1.00 1.00 Zoom LensGroup Data Group Initial Surface Focal Length 1 1 52.10 2 6 −8.15 3 1517.32 4 25 26.53

NUMERICAL EXAMPLE 4

Surface Data Surface No. r d nd νd  1 67.094 1.80 1.80610 33.3  2 31.6836.25 1.49700 81.5  1 76.853 1.80 1.80610 33.3  2 37.763 6.25 1.4970081.5  3 −701.616 0.20  4 36.812 4.10 1.60311 60.6  5 146.181 (variable) 6 30.428 1.00 1.88300 40.8  7 11.277 2.10  8 48.826 0.80 1.88300 40.8 9* 8.394 3.60 10 −22.994 0.70 1.80610 33.3 11 316.236 0.20 12 20.6712.40 1.92286 18.9 13 −91.802 (variable) 14 (stop) infinite (variable)15* 8.949 3.20 1.58313 59.4 16 −28.863 2.70 17 80.993 0.70 1.80610 33.318 8.343 0.50 19 13.373 0.70 2.00069 25.5 20 7.527 2.70 1.71999 50.2 21−30.782 0.40 22 −61.127 0.70 1.69680 55.5 23 40.314 0.30 24 (FP)infinite (variable) 25 16.450 1.80 1.58313 59.4 26 −242.919 (variable)27 infinite 1.00 1.51633 64.1 28 infinite Aspherical Surface Data  9thSurface K = −8.30991e−002, A4 = 1.64759e−005, A6 = 1.88717e−007, A8 =1.53904e−009 15th Surface K = −2.82137e−001, A4 = −1.46812e−004, A6 =3.66270e−007, A8 = −9.25941e−008, A10 = 2.12024e−009 Various Data ZoomRatio: 23.34 Wide Intermediate Telephoto Focal Length 5.12 12.18 119.63F number 2.75 3.41 5.87 Field Angle 37.09 17.65 1.86 Image Height 3.883.88 3.88 Total Lens Length 83.85 89.80 119.45 BF 9.24 12.71 6.10 d50.70 15.45 44.85 d13 24.81 12.59 2.88 d14 7.85 4.64 1.18 d24 4.39 7.5627.58 d26 7.58 11.05 4.44 d28 1.00 1.00 1.00 Zoom Lens Group Data GroupInitial Surface Focal Length 1 1 65.42 2 6 −9.23 3 15 19.20 4 25 26.49

NUMERICAL EXAMPLE 5

Surface Data Surface No. r d nd νd  1 67.094 1.80 1.80610 33.3  2 31.6836.25 1.49700 81.5  1 76.193 1.80 1.80610 33.3  2 37.010 6.30 1.4970081.5  3 −702.777 0.20  4 35.961 4.25 1.60311 60.6  5 156.906 (variable) 6 50.721 1.00 1.88300 40.8  7 10.920 2.10  8 35.606 0.80 1.88300 40.8 9 9.387 3.60 10 −36.860 0.70 1.80610 33.3 11 52.442 0.20 12 18.975 2.401.92286 18.9 13 −151.791 (variable) 14 (stop) infinity (variable) 15*11.623 3.20 1.58313 59.4 16 −83.577 4.30 17 25.898 0.80 1.92286 18.9 1810.684 0.50 19 26.374 2.00 1.77250 49.6 20 −33.636 0.40 21 131.126 0.701.60311 60.6 22 33.819 0.30 23 (FP) infinity (variable) 24* 20.173 2.001.58313 59.4 25 143.976 (variable) 26 −44.207 1.80 1.51633 64.1 27−25.803 1.51 28 infinity 1.00 1.51633 64.1 29 infinity AsphericalSurface Data 15th Surface K = 4.94320e−002, A4 = −9.60062e−005, A6 =2.70978e−007, A8 = −6.86180e−008, A10 = 2.12024e−009 24th Surface K =−1.85504e+000, A4 = 2.44173e−005, A6 = 3.02251e−007, A8 = −3.36277e−009Various Data Zoom Ratio: 19.50 Wide Intermediate Telephoto Focal Length5.13 17.55 99.93 F number 2.87 3.57 5.82 Field Angle 37.09 12.45 2.22Image Height 3.88 3.88 3.88 Total Lens Length 88.36 93.74 120.40 BF 3.173.17 3.17 d5 0.70 21.82 41.22 d13 26.37 8.79 1.95 d14 7.79 3.75 1.10 d234.48 3.06 29.25 d25 6.50 13.81 4.37 d29 1.00 1.00 1.00 Zoom Lens GroupData Group Initial Surface Focal Length 1 1 63.04 2 6 −9.33 3 15 19.96 424 39.99 5 26 116.17

NUMERICAL EXAMPLE 6

Surface Data Surface No. r d nd νd  1 67.094 1.80 1.80610 33.3  2 31.6836.25 1.49700 81.5  1 72.147 1.80 1.80610 33.3  2 35.110 6.30 1.4970081.5  3 −1895.867 0.20  4 35.096 4.20 1.60311 60.6  5 174.495 (variable) 6 52.397 1.00 1.88300 40.8  7 11.150 2.10  8 30.450 0.80 1.88300 40.8 9 9.110 3.60 10 −26.688 0.70 1.80610 33.3 11 79.207 0.20 12 20.565 2.301.92286 18.9 13 −94.030 (variable) 14 (stop) infinite (variable) 15*10.132 3.20 1.58313 59.4 16* −57.516 3.01 17 26.728 0.80 1.80610 33.3 1810.549 0.50 19 19.583 0.70 2.00330 28.3 20 7.632 2.70 1.71999 50.2 21−36.695 0.50 22 −271.272 0.70 1.58313 59.4 23 56.380 0.30 24 (FP)infinite (variable) 25* 20.173 2.40 1.77250 49.6 26 −23.872 0.60 1.8340037.2 27 124.132 (variable) 28 infinite 1.00 1.51633 64.1 29 infiniteAspherical Surface Data 15th Surface K = −6.04956e−001, A4 =−6.13122e−005, A6 = 7.43105e−007, A8 = −6.93878e−008, A10 = 2.12024e−00916th Surface K = −1.57825e+000, A4 = −1.17070e−005, A6 = 2.31644e−007,A8 = −9.19245e−010 25th Surface K = 5.70981e−002, A4 = −2.84712e−006, A6= 3.28630e−007, A8 = −6.43908e−009 Various Data Zoom Ratio: 19.13 WideIntermediate Telephoto Focal Length 5.12 17.06 97.98 F number 2.87 3.555.80 Field Angle 37.12 12.80 2.26 Image Height 3.88 3.88 3.88 Total LensLength 85.51 90.53 116.56 BF 9.27 15.83 7.59 d5 0.70 20.61 39.90 d1324.03 7.55 1.13 d14 8.72 4.68 2.03 d24 4.18 3.24 27.30 d27 7.61 14.185.93 d29 1.00 1.00 1.00 Zoom Lens Group Data Group Initial Surface FocalLength 1 1 61.25 2 6 −9.21 3 15 19.25 4 25 33.83

TABLE 1 Conditional Expression Example 1 Example 2 Example 3 Example 4Example 5 Example 6 (1) 10.0 < f1/fw < 20.0 12.387 13.659 10.166 12.76612.299 11.962 (2) 0.3 < f3a/f4 < 0.8 0.478 0.424 0.539 0.582 0.441 0.510(3) −0.6 < f3a/f3b < −0.1 −0.219 −0.249 −0.440 −0.444 −0.233 −0.216 (4)2.5 < f1/f3 < 4.5 3.265 3.632 3.007 3.407 3.158 3.182 (5) 0.2 < f3/f4 <1.0 0.534 0.485 0.653 0.725 0.499 0.569 (6) 18.0 < ft/fw < 40.0 19.07619.070 19.027 23.342 19.499 19.134

Next, an embodiment of a digital still camera which uses a zoom lensaccording to anyone of the aforementioned embodiments as a photographicoptical system, will be explained with reference to FIG. 13.

In FIG. 13, denoted at 20 is a camera body, and denoted at 21 is aphotographic optical system which is comprised of a zoom lens accordingto any one of the first to fifth embodiments described hereinbefore.Denoted at 22 is a solid-state image pickup device such as a CCD sensoror a CMOS sensor (photoelectric converting element) which is providedinside the camera body and which receives a photogenic subject imageformed by the photographic optical system 21. Denoted at 23 is a memoryfor recording the information corresponding to the photogenic subjectimage as photoelectrically converted by the solid-state image pickupdevice 22. Denoted at 24 is a finder which is comprised of a liquidcrystal display panel, for example, to observe the photogenic subjectimage formed on the solid-state image pickup device 22.

By applying a zoom lens of the present invention to an image pickupapparatus such as a digital still camera, as described above, an imagepickup apparatus being compact in size and having high opticalperformance is accomplished.

While the invention has been described with reference to the structuresdisclosed herein, it is not confined to the details set forth and thisapplication is intended to cover such modifications or changes as maycome within the purposes of the improvements or the scope of thefollowing claims.

This application claims priority from Japanese Patent Application No.2008-136616 filed May 26, 2008, for which is hereby incorporated byreference.

1. A zoom lens comprising: a first lens group of positive refractingpower; a second lens group of negative refracting power; a third lensgroup of positive refracting power; and a fourth lens group of positiverefracting power, wherein said first to fourth lens groups are providedin this order from an object side to an image side, wherein, duringzooming from a wide-angle end to a telephoto end, at least said firstlens group moves, wherein said third lens group includes, in an orderfrom the object side to the image side, a first lens sub-group ofpositive refracting power and a second lens sub-group of negativerefracting power, wherein said second lens sub-group of said third lensgroup is comprised of a single negative lens, wherein said first lenssub-group of said third lens group is moved in a direction having aperpendicular component relative to an optical axis to correct imageblur to be produced when said zoom lens vibrates, and wherein, when afocal length of said first lens group is denoted by f1 and a the focallength of the whole system at the wide-angle end is denoted by fw, aconditional expression10.0<f1/fw<20.0 is satisfied, wherein, when a focal length of said firstlens sub-group of said third lens group is denoted by f3 a and a focallength of said fourth lens group is denoted by f4, a conditionalexpression 0.3<f3 a/f4<0.8 is satisfied.
 2. A zoom lens as claimed inclaim 1, wherein, when a focal length of said first lens sub-group ofsaid third lens group is denoted by f3 a and a focal length of saidsecond lens sub-group of said third lens group is denoted by f3 b, aconditional expression −0.6<f3 a/f3 b<−0.1 is satisfied.
 3. A zoom lensas claimed in claim 1, wherein, when focal lengths of said first andthird lens groups are denoted by f1 and f3, a conditional expression2.5<f1/f3<4.5 is satisfied.
 4. A zoom lens as claimed in claim 1,wherein, when focal lengths of said third and fourth lens groups aredenoted by f3 and f4, a conditional expression 0.2<f3/f4<1.0 issatisfied.
 5. A zoom lens as claimed in claim 1, wherein, when the focallength of the whole system at the wide-angle end and the telephoto endis denoted by fw and ft, respectively, a conditional expression18.0<ft/fw<40.0 is satisfied.
 6. A zoom lens as claimed in claim 1,wherein said first lens sub-group of said third lens group includes atleast two pieces of positive lenses and one piece of negative lens.
 7. Azoom lens as claimed in claim 1, wherein said first lens group iscomprised of three lenses which are, in an order from the object side tothe image side, a negative lens, a positive lens and a positive lens. 8.A zoom lens as claimed in claim 1, wherein said second lens group iscomprised of four lenses which are, in an order from the object side tothe image side, a negative lens, a negative lens, a negative lens and apositive lens.
 9. A zoom lens as claimed in claim 1, wherein said secondlens sub-group of said third lens group is comprised of a singlenegative lens having a meniscus shape.
 10. A zoom lens as claimed inclaim 1, wherein said fourth lens group is comprised of one piece ofpositive lens or a cemented lens having a positive lens and a negativelens cemented to each other.
 11. A zoom lens as claimed in claim 1,further comprising a fifth lens group of positive refracting powerprovided at the image side of said fourth lens group, wherein said fifthsaid lens group is held stationary during the zooming.
 12. A zoom lensas claimed in claim 1, wherein said first lens sub-group of said thirdlens group is comprised of, in an order from the object side to theimage side, a positive lens, a negative lens with a surface of concaveshape at the image side, and a positive lens.
 13. A zoom lens as claimedin claim 1, wherein said first lens sub-group of said third lens groupis comprised of, in an order from the object side to the image side, apositive lens, a negative lens with a surface of concave shape at theimage side, and a cemented lens having a positive lens and a negativelens cemented to each other.
 14. A zoom lens as claimed in claim 1,wherein an image is formed on a solid-state image pickup device.
 15. Animage pickup apparatus comprising: a zoom lens as recited in claim 1;and a solid-state image pickup device configured to receive an imageformed by said zoom lens.
 16. A zoom lens comprising: a first lens groupof positive refracting power; a second lens group of negative refractingpower; a third lens group of positive refracting power; and a fourthlens group of positive refracting power, wherein said first to fourthlens groups are provided in this order from an object side to an imageside, wherein, during zooming from a wide-angle end to a telephoto end,at least said first lens group moves, wherein said third lens groupincludes, in an order from the object side to the image side, a firstlens sub-group of positive refracting power and a second lens sub-groupof negative refracting power, wherein said second lens sub-group of saidthird lens group is comprised of a single negative lens, wherein saidfirst lens sub-group of said third lens group is moved to keep aperpendicular component relative to an optical axis to correct imageblur to be produced when said zoom lens vibrates, wherein, when a focallength of said first lens group is denoted by f1 and a the focal lengthof the whole system at the wide-angle end is denoted by fw, aconditional expression 10.0<f1/fw<20.0 is satisfied, and wherein, whenfocal lengths of said first and third lens groups are denoted by f1 andf3, a conditional expression 2.5<f1/f3<4.5 is satisfied.
 17. A zoom lenscomprising: a first lens group of positive refracting power; a secondlens group of negative refracting power; a third lens group of positiverefracting power; and a fourth lens group of positive refracting power,wherein said first to fourth lens groups are provided in this order froman object side to an image side, wherein, during zooming from awide-angle end to a telephoto end, at least said first lens group moves,wherein said third lens group includes, in an order from the object sideto the image side, a first lens sub-group of positive refracting powerand a second lens sub-group of negative refracting power, wherein saidsecond lens sub-group of said third lens group is comprised of a singlenegative lens, wherein said first lens sub-group of said third lensgroup is moved to keep a perpendicular component relative to an opticalaxis to correct image blur to be produced when said zoom lens vibrates,wherein, when a focal length of said first lens group is denoted by f1and a the focal length of the whole system at the wide-angle end isdenoted by fw, a conditional expression 10.0<f1/fw<20.0 is satisfied,and wherein, when the focal length of the whole system at the wide-angleend and the telephoto end is denoted by fw and ft, respectively, aconditional expression 18.0<ft/fw<40.0 is satisfied.
 18. A zoom lenscomprising: a first lens group of positive refracting power; a secondlens group of negative refracting power; a third lens group of positiverefracting power; and a fourth lens group of positive refracting power,wherein said first to fourth lens groups are provided in this order froman object side to an image side, wherein, during zooming from awide-angle end to a telephoto end, at least said first lens group moves,wherein said third lens group includes, in an order from the object sideto the image side, a first lens sub-group of positive refracting powerand a second lens sub-group of negative refracting power, wherein saidsecond lens sub-group of said third lens group is comprised of a singlenegative lens, wherein said first lens sub-group of said third lensgroup is moved to keep a perpendicular component relative to an opticalaxis to correct image blur to be produced when said zoom lens vibrates,wherein, when a focal length of said first lens group is denoted by f1and a the focal length of the whole system at the wide-angle end isdenoted by fw, a conditional expression 10.0<f1/fw<20.0 is satisfied,and wherein said first lens group is comprised of three lenses whichare, in an order from the object side to the image side, a negativelens, a positive lens and a positive lens.
 19. A zoom lens comprising: afirst lens group of positive refracting power; a second lens group ofnegative refracting power; a third lens group of positive refractingpower; and a fourth lens group of positive refracting power, whereinsaid first to fourth lens groups are provided in this order from anobject side to an image side, wherein, during zooming from a wide-angleend to a telephoto end, at least said first lens group moves, whereinsaid third lens group includes, in an order from the object side to theimage side, a first lens sub-group of positive refracting power and asecond lens sub-group of negative refracting power, wherein said secondlens sub-group of said third lens group is comprised of a singlenegative lens, wherein said first lens sub-group of said third lensgroup is moved to keep a perpendicular component relative to an opticalaxis to correct image blur to be produced when said zoom lens vibrates,wherein, when a focal length of said first lens group is denoted by f1and a the focal length of the whole system at the wide-angle end isdenoted by fw, a conditional expression 10.0<f1/fw<20.0 is satisfied,and wherein said second lens group is comprised of four lenses whichare, in an order from the object side to the image side, a negativelens, a negative lens, a negative lens and a positive lens.
 20. A zoomlens comprising: a first lens group of positive refracting power; asecond lens group of negative refracting power; a third lens group ofpositive refracting power; a fourth lens group of positive refractingpower; a fifth lens group of positive refracting power provided at theimage side of said fourth lens group, wherein said first to fourth lensgroups are provided in this order from an object side to an image side,wherein, during zooming from a wide-angle end to a telephoto end, atleast said first lens group moves, wherein said third lens groupincludes, in an order from the object side to the image side, a firstlens sub-group of positive refracting power and a second lens sub-groupof negative refracting power, wherein said second lens sub-group of saidthird lens group is comprised of a single negative lens, wherein saidfirst lens sub-group of said third lens group is moved to keep aperpendicular component relative to an optical axis to correct imageblur to be produced when said zoom lens vibrates, and wherein, when afocal length of said first lens group is denoted by f1 and a the focallength of the whole system at the wide-angle end is denoted by fw, aconditional expression 10.0<f1/fw<20.0 is satisfied, wherein said fifthsaid lens group is held stationary during the zooming.
 21. A zoom lenscomprising: a first lens group of positive refracting power; a secondlens group of negative refracting power; a third lens group of positiverefracting power; and a fourth lens group of positive refracting power,wherein said first to fourth lens groups are provided in this order froman object side to an image side, wherein, during zooming from awide-angle end to a telephoto end, at least said first lens group moves,wherein said third lens group includes, in an order from the object sideto the image side, a first lens sub-group of positive refracting powerand a second lens sub-group of negative refracting power, wherein saidsecond lens sub-group of said third lens group is comprised of a singlenegative lens, wherein said first lens sub-group of said third lensgroup is moved to keep a perpendicular component relative to an opticalaxis to correct image blur to be produced when said zoom lens vibrates,wherein, when a focal length of said first lens group is denoted by f1and a the focal length of the whole system at the wide-angle end isdenoted by fw, a conditional expression 10.0<f1/fw<20.0 is satisfied,and wherein said first lens sub-group of said third lens group iscomprised of, in an order from the object side to the image side, apositive lens, a negative lens with a surface of concave shape at theimage side, and a cemented lens having a positive lens and a negativelens cemented to each other.